Polishing method and apparatus

ABSTRACT

This polishing method and polishing apparatus include: a polishing characteristics measurement step in which electrochemical characteristics of a slurry in relation to a material to be polished are measured; and a preparation step in which the slurry is prepared based on the measured electrochemical characteristics, wherein, in the polishing characteristics measurement step, a slurry is supplied from a slurry supply apparatus  202 , and using a sample polishing pad that is formed from the same material as the polishing pad and a sample material to be polished that is formed from the same material as the material to be polished, the electrochemical characteristics are measured both when the sample material to be polished is being polished by the sample polishing pad and when the sample material to be polished is not being polished by the sample polishing pad.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polishing method and a polishingapparatus that polishes a substrate such as a semiconductor wafer with ahigh level of precision while supplying a slurry thereto.

2. Description of Related Art

In recent years, there have been advances in the miniaturization andlevel of integration of semiconductor devices. In conjunction with this,planarization technology has become a critical problem. Because of this,chemical mechanical polishing (CMP) apparatuses are attracting attentionas processing devices that make it possible to polish to a high degreeof accuracy semiconductor wafers such as SOI substrates and the like,wafers that have a non-conductive film or metal film formed on a surfacethereof in a semiconductor integrated circuit formation process, andvarious types of semiconductor substrates such as substrates fordisplays and the like, and to thereby planarize the surface of suchsubstrates.

FIG. 8 is a block diagram showing a conventional CMP apparatus.

As is shown in FIG. 8, a CMP apparatus is provided with a CMP polishingsection 101 which has a polishing table on which a polishing pad ismounted, and has a substrate holding device that holds a substrate onwhich is formed a material to be polished; and a slurry mixture supplysection 102 that supplies a polishing agent (i.e., slurry) onto thepolishing pad. In this CMP polishing section 101, a structure isemployed in which both the substrate and the polishing table are rotatedrespectively. The surface of the substrate that is to be polished isthen brought into contact with the polishing pad, and this surface to bepolished is polished while slurry is supplied to the polishing pad fromthe slurry mixture supply section 102.

The slurry that is supplied from the slurry mixture supply section 102may be, for example, a slurry in which fine particles of SiO₂ (i.e.,abrasive grain) ranging from a micro order size to a sub micron ordersize are dispersed in an alkaline dispersion medium or in an acidicaqueous solution. The slurry is supplied from a position above the padand on the outer side of the substrate to a position between thepolishing pad and the surface of the substrate to be polished, and thesurface to be polished is polished and planarized using the chemicalaction of the slurry and the physical action of the abrasive grainpresent in the slurry. Because of this, it is necessary to keep thecomposition of the slurry constant and perform the polishing with thepolishing rate per unit time kept constant. Therefore, in order tomaintain uniform electrochemical characteristics of the slurry such as,for example, pH and concentration and the like, a CMP apparatus isprovided with an electrochemical characteristics evaluation and analysisunit 103, and a control unit 105 that controls the flow rates of thevarious chemicals that make up the slurry based on data analyzed by theevaluation and analysis unit 103.

Moreover, as is shown, for example, in Patent document 1, a structure isknown in which measurement instruments are provided in a polishingliquid supply system, and electromotive force is generated betweendissimilar metals between two electrodes that are immersed in apolishing solution contained in a polishing solution tank, and thecurrent flowing between the electrodes is monitored.

[Patent document 1] Japanese Unexamined Patent Application, FirstPublication No. 2004-6499

SUMMARY OF THE INVENTION

Parameters for the electrochemical characteristics of the material to bepolished in the slurry include spontaneous potential, corrosionpotential, corrosion current and the like, and it is known that there isa considerable difference in these characteristics between when thematerial to be polished is in a stationary state (i.e., is not beingpolished) inside the slurry, and when it is being polished. Accordingly,determining the optimum slurry composition simply from theelectrochemical characteristics in a stationary state, as in Patentdocument 1, does not necessarily reflect the polishing conditions for anobject being polished during an actual CMP process, and achieving ahighly reliable CMP process is difficult.

Moreover, the polishing material that is formed on the substrate surfaceis not formed by a single material, but, as in the case of a wiringpattern, for example, is formed by stacking non-conductive films, metalfilms, and the like. In particular, what is known as a Damascene processis used as a process for forming the wiring of a semiconductor device.In this process, wiring metal is embedded inside recessed portions forwiring such as trenches and via holes that are provided in anon-conductive film. In the Damascene process, in order to preventspreading of the wiring metal and secure good adhesion, the wiring metalis embedded after a barrier film has been formed inside the wiringrecessed portions. Because of this, initially, the CMP process performsthe polishing of a single material, however, in the final stages of theCMP process, a plurality of types of material are exposed. As a result,complex electrochemical phenomena are generated at the polishingsurface, and a situation is created in which defect formation such ascorrosion occurs easily. Accordingly, there is now an even greater needthan hitherto for slurry characteristics to be stabilized, and a CMPapparatus is required that can maintain these characteristics to a highlevel of accuracy.

Accordingly, the present invention was conceived in view of the abovedescribed circumstances, and it is an object thereof to provide apolishing method and polishing apparatus that maintain theelectrochemical characteristics of slurries for various materials to bepolished to a high level of accuracy and make precise polishingpossible.

In order to achieve the above described object, a first aspect of thepresent invention is a polishing method in which, at the same time as aslurry is being supplied to a surface of a polishing pad by a slurrysupply apparatus, a material to be polished is polished by moving thepolishing pad relatively to the material to be polished that is formedon a substrate surface while also bringing the polishing pad and thematerial to be polished into mutual contact, and that includes: apolishing characteristics measurement step in which electrochemicalcharacteristics of the slurry in relation to the material to be polishedare measured; and a preparation step in which the slurry is preparedbased on the measured electrochemical characteristics, wherein in thepolishing characteristics measurement step, a slurry is supplied fromthe slurry supply apparatus, and using a sample polishing pad that isformed from the same material as the polishing pad and a sample materialto be polished that is formed from the same material as the material tobe polished, the electrochemical characteristics are measured both whenthe sample material to be polished is being polished by the samplepolishing pad and when the sample material to be polished is not beingpolished by the sample polishing pad. According to this structure, it ispossible to quantitatively ascertain in all states during a polishingstep the electrochemical reaction state between a slurry and a materialbeing polished. Namely, by supplying slurry from the slurry supplyapparatus separately from the actual polishing step, and using a samplepolishing pad and a sample material to be polished, measuring theelectrochemical characteristics both when the sample material to bepolished is being polished and when the sample material to be polishedis not being polished, it is possible to ascertain the behavior of thesame electrochemical characteristics as those present in the actualpolishing step. Because of this, it is possible to determine the optimumslurry characteristics in accordance with the polishing conditions. Inaddition, by preparing a slurry based on the measured electrochemicalcharacteristics, it is possible to control the electrochemicalcharacteristics of the slurry relative to the material to be polished toa high level of accuracy. Accordingly, it is possible to predict theoccurrence of unanticipated faults such as corrosion of the material tobe polished, over-polishing, defect creation, and the like, before thesefaults actually occur, and thus perform highly accurate polishing.Moreover, it is possible to always maintain optimum control of thecomposition ratio and the like of a slurry, and achieve a stabilizationof the polishing process. Furthermore, it also becomes possible tochoose an optimum slurry using these evaluations, so that thedevelopment of an optimum process in an even shorter time becomespossible.

In a preferred aspect of the present invention, in the polishingcharacteristics measurement step, the electrochemical characteristicsare measured using a plurality of the sample materials to be polishedthat correspond to a plurality of the sample materials to be polishedthat are formed on the substrate surface.

According to this structure, even if a plurality of types of material tobe polished are exposed on a substrate surface, it is possible toascertain the reactivities of the electrochemical characteristics of theslurries in relation to each individual one of the materials to bepolished. Accordingly, it is possible to predict the occurrence ofunanticipated faults such as corrosion of the material to be polished,over-polishing, defect creation, and the like, before these faultsactually occur, and thus perform highly accurate polishing.

In a preferable aspect of the present invention, in the polishingcharacteristics measurement step, the corrosion potentials of each ofthe plurality of sample materials to be polished are measured, and whenthe corrosion potential of a primary material is measured in thepolishing characteristics measurement step as being lower than thecorrosion potential of a secondary material from among the respectivesample materials to be polished, the composition of the slurry isadjusted in the preparation step such that the corrosion potential ofthe secondary material is set within a passive state area or a stablearea of a Pourbaix diagram of the primary material.

According to this structure, when the corrosion potential of thesecondary material is higher than the corrosion potential of the primarymaterial, the composition of the slurry is adjusted such that thecorrosion potential of the secondary material is set within a passivestate area or a stable area on a Pourbaix diagram of the primarymaterial. As a result, the primary material does not get drawn insidethe corrosion area by the potential gradient in boundary portionsbetween the primary material and the secondary material, and the primarymaterial is reliably polished within the passive state area or thestable area. Accordingly, it is possible to prevent corrosion of theprimary material.

In a preferable aspect of the present invention, the pH of the slurry isadjusted in the preparation step.

According to this structure, by adjusting the pH of the slurry, It ispossible to set the corrosion potential of the secondary material withina passive state area or a stable area on a Pourbaix diagram of theprimary material. As a result, the primary material does not get drawninside the corrosion area, and the primary material can be reliablypolished within the passive state area or the stable area.

Another aspect of the present invention is a polishing apparatus that isprovided with a polishing pad, and a slurry supply apparatus thatsupplies slurry onto the polishing pad, in which, at the same time asthe slurry is being supplied by the slurry supply apparatus, a materialto be polished is polished by moving the polishing pad relatively to thematerial to be polished that is formed on a substrate surface while alsobringing the polishing pad and the material to be polished into mutualcontact, wherein there are provided a polishing characteristicsmeasurement section that measures electrochemical characteristics of theslurry in relation to the material to be polished, and a preparationsection that prepares the slurry based on the measured electrochemicalcharacteristics, and wherein a slurry is supplied from the slurry supplyapparatus, and a sample material to be polished that is formed from thesame material as the material to be polished and a sample polishing padthat is formed from the same material as the polishing pad are held inthe polishing characteristics measurement section, and the polishingcharacteristics measurement section measures the electrochemicalcharacteristics both when the sample material to be polished is beingpolished by the sample polishing pad and when the sample material to bepolished is not being polished by the sample polishing pad.

According to this structure, it is possible to quantitatively ascertainin all states during a polishing step the electrochemical reaction statebetween a slurry and a material being polished. Namely, as a result ofslurry being supplied from the slurry supply apparatus separately fromthe actual polishing step, and the electrochemical characteristics bothwhen the sample material to be polished is being polished by a samplepolishing pad and when the sample material to be polished is not beingpolished, it is possible to ascertain the behavior of the sameelectrochemical characteristics as those present in the actual polishingstep. Because of this, it is possible to determine the optimum slurrycharacteristics in accordance with the polishing conditions. Inaddition, by preparing a slurry based on the measured electrochemicalcharacteristics, it is possible to control the electrochemicalcharacteristics of the slurry relative to the material to be polished toa high level of accuracy. Accordingly, it is possible to predict theoccurrence of unanticipated faults such as corrosion of the material tobe polished, over-polishing, defect creation, and the like, before thesefaults actually occur, and thus perform highly accurate polishing.Moreover, it is possible to always maintain optimum control of thecomposition ratio and the like of a slurry, and achieve a stabilizationof the polishing process. Furthermore, it also becomes possible tochoose an optimum slurry using these evaluations, so that thedevelopment of an optimum process in an even shorter time becomespossible.

In a preferable aspect of the present invention, a plurality of thesample materials to be polished that correspond to a plurality of thesample materials to be polished that are formed on the substrate surfaceare held in the polishing characteristics measurement section.

According to this structure, even if a plurality of types of material tobe polished are exposed on a substrate polishing surface, it is possibleto ascertain the reactivities of the electrochemical characteristics ofthe slurries in relation to each individual one of the materials to bepolished. Accordingly, it is possible to predict the occurrence ofunanticipated faults such as corrosion of the material to be polished,over-polishing, defect creation, and the like, before these faultsactually occur, and thus perform highly accurate polishing.

According to the present invention, it is possible to quantitativelyascertain in all states during a polishing step the electrochemicalreaction state between a slurry and a material being polished. Namely,by supplying slurry from a slurry supply apparatus separately from anactual polishing step, and using a sample polishing pad and a samplematerial to be polished, measuring the electrochemical characteristicsboth when the sample material to be polished is being polished and whenthe sample material to be polished is not being polished, it is possibleto ascertain the behavior of the same electrochemical characteristics asthose present in the actual polishing step. Because of this, it ispossible to determine the optimum slurry characteristics in accordancewith the polishing conditions. In addition, by preparing a slurry basedon the measured electrochemical characteristics, it is possible tocontrol the electrochemical characteristics of the slurry relative tothe material to be polished to a high level of accuracy. Accordingly, itis possible to predict the occurrence of unanticipated faults such ascorrosion of the material to be polished, over-polishing, defectcreation, and the like, before these faults actually occur, and thusperform highly accurate polishing. Moreover, it is possible to alwaysmaintain optimum control of the composition ratio and the like of aslurry, and achieve a stabilization of the polishing process.Furthermore, it also becomes possible to choose an optimum slurry usingthese evaluations, so that the development of an optimum process in aneven shorter time becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a CMP apparatus according to anembodiment of the present invention.

FIG. 2 is a perspective view showing essential portions of a CMPapparatus according to an embodiment of the present invention.

FIG. 3 is a schematic structural view of a polishing characteristicsmeasurement portion according to an embodiment of the present invention.

FIG. 4 is a process diagram of a CMP apparatus according to anembodiment of the present invention.

FIG. 5 is a graph showing polarization characteristics during polishingand not during polishing of three types of materials for polishing.

FIG. 6 is a graph showing OCP changes, and shows corrosion potentialduring polishing and not during polishing of the respective materialsfrom the graph of polarization characteristics shown in FIG. 5.

FIG. 7 is a Pourbaix diagram when the material B is being polished.

FIG. 8 is a block diagram showing a conventional CMP.

BRIEF DESCRIPTION OF THE REFERENCE NUMERALS

-   -   44 a to 44 c . . . Sample materials (sample materials to be        polished)    -   47 . . . Polishing pad (sample polishing pad)    -   50 . . . Slurry    -   64 . . . Barrier film (material to be polished)    -   65 . . . Polishing pad    -   66 . . . Conductive film (material to be polished)    -   200 . . . CMP apparatus (polishing apparatus)    -   201 . . . CMP polishing section    -   202 . . . Slurry supply device    -   203 . . . Polishing characteristics measurement section    -   W . . . Substrate

DETAILED DESCRIPTION OF THE INVENTION

Next, embodiments of the present invention will be described withreference made to the drawings.

Firstly, a CMP apparatus according to the present embodiment will bedescribed.

(CMP Apparatus)

FIG. 1 is a block diagram showing a CMP apparatus according to thepresent invention, and FIG. 2 is a perspective view showing essentialportions of a CMP apparatus.

As is shown in FIG. 1, a CMP 200 is formed by a CMP polishing section201, a slurry mixture supply section 202, a polishing characteristicsmeasurement section 203, and a control unit 207 that controls the slurrymixture supply section 202 and polishing characteristics measurementsection 203.

As is shown in FIG. 2, the CMP polishing section 201 is provided with apolishing object holding device 25 that removably holds a substrate W onwhich are formed materials for polishing (i.e., a barrier film 64 and awiring film 66; see FIG. 4—these are described below) such that asurface for polishing is facing downwards, and a polishing table 26 thatis positioned facing the substrate W that is being held on the polishingobject holding device 25. A polishing pad 65 whose aperture diameter islarger than the aperture diameter of the substrate W is mounted on thepolishing table 26. This polishing pad 65 is formed, for example, frompolyurethane or the like, and bumps and indentations and multiple poresand the like are formed on a surface thereof.

Returning to FIG. 1, the slurry mixture supply section 202 mixes aslurry that has been supplied under optimum conditions (i.e., mixtureratios, flow rate, and the like) by a slurry flow rate control unit 206(described below), and then supplies it onto the polishing pad 65. Aslurry that is formed by dispersing fine particles of SiO₂ (i.e.,abrasive grain) ranging from a micro order size to a sub micro ordersize in ammonium persulfate ((NH₄)₂S₂O₈) is used as the slurry of thepresent embodiment. By using ammonium persulfate as a solvent in thismanner, it is possible to obtain an excellent polishing speed. Note thatin addition to the above described materials, it is also possible to mixin corrosion inhibitors, complexing agents, and oxidizing agents and thelike such as benzotriazole (BTA).

The control unit 207 is provided with an electrochemical characteristicsevaluation and analysis unit 204, a central processing unit CPU 205, andthe slurry flow rate control unit 206.

The electrochemical characteristics evaluation and analysis unit 204 isformed by a computer-controlled potentiostat/galvanostat or the like,and converts electrochemical characteristics obtained by the polishingcharacteristics measurement section 203 into quantified data which itthen outputs to the central processing unit CPU 205.

The central processing unit CPU 205 receives the electrochemicalcharacteristics data that has been converted by the electrochemicalcharacteristics evaluation and analysis unit 204. It then refers toelectrochemical characteristics and the like in an individual andtypical composition in a basic slurry that has been prepared in advance,and calculates the compositions of each component of a slurry structurethat will provide the optimum electrochemical characteristic conditions.

The slurry flow rate control unit 206 supplies the respective slurrystructural components under the optimum conditions (i.e., mixing ratios,flow rates, and the like) based on the compositions of the slurrystructural components calculated by the central processing unit CPU 205.

In this manner, a structure is employed in which the slurry compositionis controlled by the electrochemical characteristics evaluation andanalysis unit 204, the central processing unit CPU 205, and the slurryflow rate control unit 206, and is supplied to the slurry mixture supplysection 202.

Here, the aforementioned polishing characteristics measurement sectionis described in detail below. FIG. 3 is a schematic structural view of apolishing characteristics measurement section.

As is shown in FIG. 3, the polishing characteristics measurement section203 is provided with a storage tank 31 that has a plurality of (forexample, three) aperture portions 32 a to 32 c formed in a bottomsurface thereof. A plurality of sample materials to be polished(referred to below as sample materials) 44 a to 44 c are held below thisstorage tank 31. These sample materials 44 a to 44 c are the samematerial as the material to be polished that is formed on theaforementioned substrate W and, for example, copper (Cu), tantalum (Ta),and ruthenium (Ru) and the like are used for the sample materials. Therespective sample materials 44 a to 44 c are plate-shaped components,and are pressed towards the bottom surface of the storage tank 31 withO-rings 49 sandwiched between the respective sample materials and thestorage tank 31, so that the aperture portions 32 a to 32 c are blockedoff. Namely, the sample materials 44 a to 44 c are formed such that thesurfaces thereof are exposed to the interior of the storage tank 31 viathe aperture portions 32 a to 32 c.

A sample slurry is stored in the storage tank 31. This sample slurry hasthe same composition as the slurry that is supplied to theaforementioned CMP polishing section 201, and is supplied from theslurry mixture supply section 202 in the same way as the slurry suppliedto the CMP polishing section 201.

A polishing section 43 is immersed inside the storage tank 31. Thepolishing section 43 is provided with a rotation shaft 48. The rotationshaft 48 is a circular column-shaped component, and is constructed suchthat it is able to be rotated around an axis of the rotation shaft 48 bya drive apparatus (not shown). Moreover, the rotation shaft 48 isconstructed such that it is moved by a drive apparatus inside thestorage tank 31 as far as a position facing the respective samplematerials 44 a to 44 c (shown by the arrow in FIG. 3), and such that itis able to move in a direction towards or away from the surfaces of therespective sample materials 44 a to 44 c.

A polishing pad 47 (i.e., a sample polishing pad) is mounted on a distalend of the rotation shaft 48. This polishing pad 47 is a disk-shapedcomponent that has the same structure as that of the polishing pad ofthe above described CMP polishing section 201. By lowering the rotationshaft 48 as it is being rotated, the polishing pad 47 is pressed againstthe surface of the respective sample materials 44 a to 44 c, and thesurfaces of the sample materials 44 a to 44 c and the polishing pad 47move relatively to each other so that the sample materials 44 a to 44 cbecome polished. Namely, a structure is employed in which, in thepolishing characteristics measurement section 203, polishing is carriedout on the sample materials 44 a to 44 c, which are the same as thematerials to be polished that are to be actually polished by the CMPpolishing section 201, using a sample slurry that has the samecomposition as the slurry used by the CMP polishing section 201.

Moreover, a reference electrode 45 that is formed, for example, fromsilver/silver chloride (Ag/AgCl), and an auxiliary electrode 46 that isformed, for example, from platinum (Pt) are immersed inside the storagetank 31.

In addition, using the respective sample materials 44 a to 44 c asworking electrodes, a potentiostat that is formed by a three-electrodesystem is constructed by sequentially applying voltage between thereference electrode 45 and auxiliary electrode 46 and any one of therespective sample materials 44 a to 44 c using a power supply (notshown). As a result, current flows between the three electrodes, and itis possible to measure the electrochemical characteristics of the sampleslurry with regard to each of the sample materials 44 a to 44 c insidethe storage tank 31. In this manner, in the polishing characteristicsmeasurement section 203, the electrochemical characteristics of a sampleslurry are measured under the same polishing conditions as those presentin the CMP polishing section 201 both when the respective samplematerials 44 a to 44 c are being polished and when they are not beingpolished.

(Polishing Method)

Next, the polishing method of the present embodiment will be described.

Firstly, the film structure of a substrate which is to be polished ofthe present embodiment will be described. FIG. 4 is a process diagram ofa CMP apparatus according to an embodiment of the present invention.

As is shown in FIG. 4A, an interlayer non-conductive film 62 that isformed from a non-conductive material such as SiO₂, SiOF, SiOC, or aLow-k material (i.e., a low dielectric constant non-conductive film) orthe like is formed on a surface of a substrate W that is formed fromsilicon or the like. A recessed portion 63 for wiring formation isformed in a surface of the interlayer non-conductive film 62. A barrierfilm (i.e., a material to be polished) 64 is formed at a thickness ofapproximately 10 nm on the surface of the interlayer non-conductive film62 including the recessed portion 63. The barrier film 64 is provided inorder to prevent the metal material of the wiring film 66 (describedbelow) spreading over the substrate W, and in order to improve theadhesion between the wiring film 66 and the interlayer non-conductivefilm 62. The barrier film 64 is conventionally formed solely fromtantalum (Ta) or from a Ta compound, however, recently, it is beingformed by sandwiching a ruthenium (Ru) layer which has excellentconductivity between a pair of tantalum (Ta) layers which have excellentadhesiveness.

A conductive film (i.e., a material to be polished) 66 that is formedfrom (Cu) is formed at a thickness of approximately 500 to 1000 nm onthe surface of the barrier film 64. When this wiring film 66 is formedby means of an electroplating method, then a seed film (not shown) isformed first on the surface of the barrier film 64 so as to provide anelectrode for the electroplating. Note that a recessed portion 67 havinga height of approximately 300 nm and a width of approximately 100 μm isformed on the surface of the wiring film 66 so as to match the recessedportion 63 in the interlayer non-conductive film 62. Note also that thedimensions of the wiring formation recessed portions shown here areshown as examples thereof. Moreover, in the present embodiment, adescription is given of when copper is used as the wiring film 66,however, in addition to copper, examples of a conductive substance to bepolished include conductive metal materials such as aluminum (Al),silver (Ag), gold (Au), nickel (Ni), tungsten (Zn), ruthenium (Ru), andalloys of these.

Because only the wiring film 66 with which the inner side of therecessed portion 63 of the interlayer non-conductive film 62 is filledis used as metal wiring, the wiring film 66 and the barrier film 64 thatare formed on the outside of the recessed portion 63 are not required.Moreover, because a plurality of wires are stacked via the interlayernon-conductive film 62, when the wiring film 66 and the barrier film 64have been removed, it is necessary for the surface of the wiring film 66in the recessed portion 63 and the surface of the interlayernon-conductive film 62 to be located on the same plane, and for thesurface of the substrate W to be planarized. Therefore, surplus metalwiring (i.e., the wiring film 66 and the barrier film 64) are removedand planarized by CMP polishing.

As is shown in FIG. 4B, in CMP polishing, a slurry 50 is interposedbetween the metal film on the surface of the substrate W and thepolishing pad 65, and the substrate W and polishing pad 65 are moved(i.e., rotated) relatively while the surface of the substrate W ispressed against the polishing pad 65, thereby polishing the surface ofthe metal film. At this time, abrasive grain and oxidizing agent and thelike are contained in the slurry 50 and an oxide film is formed on thesurface of the polishing material by this oxidizing agent. Because theoxide film that is formed on an upper portion H of the polishingmaterial (i.e., the outer side of the recessed portion 63) is removed bythe contact with the polishing pad, the polishing material on the upperportion H is polished. In contrast to this, an oxide film 70 that isformed on a lower portion L of the polishing material (i.e., the innerside of the recessed portion 63) does not come into contact with thepolishing pad, it is not removed in the polishing material of the lowerportion L is not polished. As a result, as is shown in FIG. 4C to 4E,the height differences in the polished surfaces (i.e., the recessedportion 67) are gradually eliminated.

The polishing method of the present embodiment is principally made up ofa polishing characteristics measurement step, steps to prepare both bulkand clear slurries, bulk and clear polishing steps, a step to prepare abarrier slurry, and a barrier polishing step. Namely, polishing of thewiring film 66 is performed in two polishing stages, namely bulkpolishing (see FIG. 4B) and clear polishing (see FIG. 4C) correspondingto the thickness of the film which changes as the polishing progresses.Next, as is shown in FIG. 4D, a barrier polishing step is performed inwhich the wiring film 66 and the barrier film 64 are exposed on the samepolishing surface plane, and these two are both polished simultaneously.

(Polishing Characteristics Measurement Step)

Parameters for the electrochemical characteristics of the material to becoated in the slurry include spontaneous potential, corrosion potential,corrosion current and the like, and it is known that there is aconsiderable difference in these characteristics between when thematerial to be coated is in a stationary state (i.e., is not beingpolished) inside the slurry, and when it is being polished. Accordingly,determining the optimum slurry composition simply from theelectrochemical characteristics in a stationary state, as is the caseconventionally, does not necessarily reflect the polishing conditionsfor an object being polished during an actual CMP process, and achievinga highly reliable CMP process is difficult.

Moreover, the polishing material that is formed on the substrate surfaceis not formed by a single material, but, as in the case of a wiringpattern, for example, is formed by superposing non-conductive films,metal films, and the like. In particular, in the aforementionedDamascene process, initially, the CMP process performs the polishing ofa single material, however, in the final stages of the CMP process, aplurality of types of material are exposed. As a result, complexelectrochemical phenomena are generated at the polishing surface, and asituation is created in which defect formation such as corrosion occurseasily. Accordingly, there is now an even greater need than hitherto forslurry characteristics to be stabilized, and a CMP apparatus is requiredthat can maintain these characteristics to a high level of accuracy.

The applicants of the present invention made measurements using themethod described below of the electrochemical characteristics ofslurries in relation to materials to be polished. Firstly, the specificelectrochemical characteristics to be measured are broadly divided intotwo types. One type is polarization characteristics, and the other typeis open circuit potential (OCP).

FIG. 5 shows polarization characteristics when three types of polishingmaterials are being polished and are not being polished. While thepotential is being scanned from a low potential side to a high potentialside the current is measured, and the polarization characteristics areplotted between a logarithmic scale of the current density and thepotential. In addition, as the polishing materials used in thisexperiment, ruthenium (Ru) is used for sample A, copper (Cu) is used forsample B, and tantalum (Ta) is used for sample C, while ammoniumpersulfate ((NH₄)₂S₂O₈) is used as an oxidizer in the slurry solvent.

As is shown in FIG. 5, it was found that as the potential was increasedfrom a low potential, the current density was on a decreasing trend ineach of the samples A through C. In addition, it was found that at aparticular predetermined potential, the current density maintained aminimum value, and as the potential was further increased from thatpoint, the current density changed to an increasing trend. On the lowpotential side of the potential where the current density is at theminimum a reductive reaction occurs, while on the high potential sidethereof an oxidation reaction occurs. Specifically, in the reductivereaction on the low potential side a phenomenon occurs in which, forexample, hydrogen ions contained in the slurry bond with electrons togenerate hydrogen gas, and the material to be polished is placed in astable state. In contrast, in the oxidation reaction on the highpotential side, the surface of the polishing material is oxidized andionized, and melts in the slurry.

Here, the potential where the current density is at the minimum value iscalled the corrosion potential (Ecorr), while the current density atthis time is called the corrosion current density (icorr).

Furthermore, the current density for sample A is the largest both duringpolishing and when there is no polishing, and next comes sample B andthen sample C. From this data, it was found that sample A had thegreatest reactivity with the slurry, while that of sample C was thesmallest. Moreover, when the current densities during polishing and whenthere was no polishing were compared, it was found that the currentdensity was greater during polishing in each of the three samples A toC. This shows that the surface layer was erased by the polishing toexpose a new surface, and that this new surface provided a vigoroussurface reaction.

Next, in the same way as the current density, the potential for sample Ais the largest both during polishing and when there is no polishing, andnext comes sample B and then sample C. Moreover, in regard to thepotentials for each polishing material, in the cases, for example, ofmaterials A and C, there was a shift towards the lower potential sideand the higher current density side during polishing in comparison towhen polishing was not being performed. However, in material B, it wasfound that there was a shift to the high potential side duringpolishing. In this manner, by comparing the material B, and thematerials A and C, it was found that there were differences in thebehavior of the reactions during polishing and when polishing was notbeing performed.

FIG. 6 is a graph showing OCP changes in which the horizontal axisindicates time and the vertical axis indicates OCP. The OCP correspondsto the corrosion potentials when polishing was and was not beingperformed on the respective materials A through C for the polarizationcharacteristics shown in FIG. 5.

As is shown in FIG. 6, for the OCP when polishing is not beingperformed, the material A was in a noble state (namely, the potentialwas highest), while the material C was in a base state (namely, thepotential was lowest).

As is shown in FIG. 6, the value of the OCP decreased in material A andmaterial C following the progression from a non-polishing state to apolishing state, however, this value increased in material B. Incontrast, the value of the OCP increased in material A and material Cfollowing the progression from a polishing state to a non-polishingstate, however, this value decreased in material B. As a result, in anon-polishing state, a sizable potential difference was generatedbetween material A and material B. From these changes, it was foundthat, for example, if material A and material B were present in the sameslurry, then material B was in a base potential state and was easilycorrodible.

FIG. 7 shows a Pourbaix diagram (i.e., showing potential—pH) of materialB, that is the primary material for forming the metal wiring. In thiscase, the potential of the primary material B is lower than thepotential b of the material A and, moreover, is in a stable region. Asis shown in FIG. 7, in a slurry in which the pH is α, when a secondarymaterial (for example, the material A) which is nobler than the materialB which is the primary material is exposed to the polishing surface andis present in the same slurry, namely, when this secondary material isin the same state as the wiring being processed, then the potential a ofthe material B is pulled to the potential b of the material A and thepotential of the material B increases. The potential of the primarymaterial B approaches particularly close to the potential of thematerial A in a portion close to the contact portion between thematerial B and the material A. This is due to the potential gradientbetween the material A and the material B. Moreover, the greater thepotential difference between the material A and the material B, thegreater the possibility that the potential b of the material A will bepresent in a corrosion area.

Namely, when there is a sizeable potential difference between thematerials A and B, and the potential b of the material A is present in acorrosion area, there is a possibility that the potential of thematerial B will also be pulled towards the corrosion area. As a resultof this, there is also a possibility that the material B which is theprimary material will become corroded. Namely, even if a slurry isprepared having a composition in which the material B was set inside thestable area prior to polishing, then depending on the polishingconditions there is a possibility that the potential of the material Bwill increase as far as a corrosion area.

In this manner, because the potential difference between material B andmaterial A is small during polishing and large when polishing is notbeing performed, it can be determined that there is a need to payattention to the occurrence of corrosion in the material B at thosepoints in time when polishing is halted and there is a switch to anon-polishing state, and when abrupt changes occur in the OCP such as atboundary portions and the like between material A and material B.

In order to prevent corrosion of the material B, in the above describedPourbaix diagram (see FIG. 7), it is sufficient if the composition ofthe slurry is adjusted such that the potential of material A (forexample, Ru) is kept within a passive state area or the stable area.Namely, the pH of the slurry is lowered so that it is kept within therange of β in FIG. 7. The pH may be lowered by mixing an acidic materialsuch as sulfuric acid or hydrochloric acid in the slurry, or by dilutingthe concentration of alkaline material in the slurry. As a result, evenif the material A is nobler than the material B, and the potential ofthe material B is pulled towards the material A side by the potentialgradient between the material A and the material B, the material B doesnot get drawn inside the corrosion area. Namely, by preparing a slurrythat has a composition whereby the material A, which is a noble materialin comparison to the material B, is set within a passive state area or astable area, it is possible to prevent the material B, which is theprimary material, from being corroded.

Here, in consideration of the above described phenomenon, the applicantsof the present invention discovered that it is possible to ascertain inadvance the electrochemical characteristics of an actual polishing stepby performing polishing in the polishing characteristics measurementsection 203 separately from the actual polishing step under the sameconditions as those for the CMP polishing section 201. By ascertainingthe electrochemical characteristics of a slurry towards a material to bepolished, it is possible to detect that it has not been possible toprepare a predetermined slurry because of a fault in the slurry mixturesupply section 202 or the like.

Firstly, as is shown in FIGS. 1 to 4E, prior to the polishing by the CMPpolishing section 201, changes in the electrochemical characteristics ofa sample slurry towards a material to be polished are measured inadvance in the polishing characteristics measurement section 203 (i.e.,a polishing characteristics measurement step). Note that the measurementof the polishing characteristics may be performed prior to the start ofpolishing operations each day, or prior to the start of polishingoperations of each lot, or prior to the start of the polishing operationon each substrate. Measurements may also be made during a polishingoperation.

Specifically, changes in the electrochemical characteristics of a sampleslurry both when the respective sample materials 44 a to 44 c were beingpolished and when these were not being polished by the sample polishingpad 47 are sequentially measured. The various types of electrochemicalcharacteristics that were obtained by the polishing characteristicsmeasurement section 203 are converted into quantified data in theelectrochemical characteristics evaluation and analysis unit 204, andthis is then output to the central processing unit CPU 205. The centralprocessing unit CPU 205 calculates optimum slurry composition data basedon the data received from the electrochemical characteristics evaluationand analysis unit 204.

Next, a slurry is prepared based on the electrochemical characteristicsdata during the polishing of the sample material 44 a (i.e., copper)that was measured by the polishing characteristics measurement section203 prior to the bulk polishing and clear polishing of the metal wiringlayer, namely, prior to performing polishing in a state in which onlythe wiring film 66 that is to form the metal wiring layer (i.e., theprimary material) is exposed (i.e., bulk and clear slurry preparationstep). Specifically, in the slurry flow rate control unit 206, slurrystructural components are supplied at the optimum conditions based onthe optimum slurry composition data calculated by the central processingunit CPU 205. In addition, the slurry that is supplied at the optimumconditions is mixed in the slurry mixture supply section 202 and is thensupplied onto the polishing pad 65.

Next, in the CMP polishing section 201, polishing of a material to bepolished is performed using the above-described polishing method (i.e.,a bulk and clear polishing step; see FIG. 4B and FIG. 4C). At this time,it is preferable for the polishing to be performed while changes in theelectrochemical characteristics of the slurry in relation to the wiringfilm 66 in the CMP polishing section 201 are measured. In addition, whenthe bulk polishing and clear polishing have ended, the wiring film 66and the barrier film 64 are exposed on the same plane of the polishingsurface.

Next, prior to the barrier polishing to simultaneously polish the wiringfilm 66 and the barrier film 64 that are exposed on the same plane ofthe polishing surface, a slurry is prepared for the barrier polishing(i.e., barrier slurry preparation step).

Firstly, in the above-described polishing characteristics measurementstep, it is confirmed whether or not a noble material whose potential ishigher than the potential of the wiring film 66 (i.e., the primarymaterial), which is the portion of the structural materials of thebarrier film 64 (i.e., the secondary material) that forms the wiring, ispresent on the polishing surface.

If a structural material that will make the wiring film 66 a base is notpresent on the polishing surface, then, if, for example, of thestructural materials making up the barrier film 64, only the tantalum(material C in FIG. 6) which has a lower potential than that of thecopper (Cu) which forms the wiring film 66 is exposed, a slurry that hasbeen prepared having the same composition as that during normal barrierpolishing is supplied. A barrier polishing step is then performed tosimultaneously polish the copper (Cu) of the wiring film 66 and thetantalum (Ta) of the barrier film 64. Polishing is then continued inthis state. At this time, the Ta is the base material relative to theCu, however, because a solid oxide film is formed on the surface of theTa, corrosion of the Ta does not become a problem.

In contrast, if a structural material that will make the wiring film 66a base is present on the polishing surface, then, if, for example, ofthe structural materials making up the barrier film 64, ruthenium (Ru)which has a higher potential than that of the copper (Cu) which formsthe wiring film 66 is exposed, it is determined that there is apossibility that the wiring film 66 will be corroded. In addition, aslurry is prepared that has a composition that does not cause the wiringfilm 66 to be corroded (i.e., barrier slurry preparation step).

Specifically, in the above described Pourbaix diagram (see FIG. 7), thecomposition of the slurry is adjusted such that the potential of theruthenium (Ru) which is the material A is kept within a passive statearea or the stable area. Namely, the pH of the slurry is lowered so thatthe potential of the material A is kept within the range of β in FIG. 7.As a result, even if the Ru is nobler than the Cu, and the potential ofthe Cu is pulled towards the Ru side by the potential gradient betweenthe Ru and the material Cu, the Cu does not get drawn inside thecorrosion area. Namely, by preparing a slurry that has a compositionwhereby the Ru, which is a noble material in comparison to the Cu, isset within a passive state area or a stable area, it is possible toprevent the wiring film 66, which is the primary material, from beingcorroded.

Note that in addition to the above described method of setting thepotential of the Ru within a passive state area or a stable area, it isalso possible to make the adjustment using a corrosion inhibitor such asBTA. For example, by increasing the proportion of BTA in the preparedslurry composition, it is possible to enlarge the passive state area inthe Pourbaix diagram. As a result, because there is an increase in theboundary potential between the corrosion area and the passive statearea, the Ru is easily kept in the passive state area or stable area. Inaddition, because it is possible to enlarge the range of range of β inFIG. 7, the above-described pH based adjustments can be easily made.

Finally, a barrier polishing step is then performed (see FIG. 4D) tosimultaneously polish the copper (Cu) of the wiring film 66 and theruthenium (Ru) of the barrier film 64.

In this manner, according to the above-described present embodiment, astructure is employed in which there are provided a polishingcharacteristics measurement step to measure electrochemicalcharacteristics of a slurry in relation to a material to be polished(i.e., the wiring film 66 and the barrier film 64), and a preparationstep to prepare a slurry based on the measured electrochemicalcharacteristics, and in the polishing characteristics measurement step,a sample slurry having the same composition as that of the slurry issupplied from the slurry supply apparatus 202 separately from the actualpolishing step, and using the polishing pad 47 and the sample materials44 a to 44 c, the electrochemical characteristics are measured bothduring polishing and non-polishing of the sample materials 44 a to 44 cthat are formed from the same materials as the materials to be polished.

According to this structure, it is possible to quantitatively ascertainin all states during a polishing step the electrochemical reaction statebetween a slurry and a material being polished. Namely, by performingpolishing in the polishing characteristics measurement section 203 underthe same polishing conditions as those present in the CMP polishingsection 201 separately from the actual polishing step performed by theCMP polishing section 201, it is possible to ascertain the behavior ofthe same electrochemical characteristics as those present in the actualpolishing step. Because of this, it is possible to determine the optimumslurry characteristics in accordance with the polishing conditions. Inaddition, by preparing a slurry based on the measured electrochemicalcharacteristics, it is possible to control the electrochemicalcharacteristics of the slurry relative to the material to be polished toa high level of accuracy.

When the corrosion potential of the Ru (i.e., the secondary material) ishigher than the corrosion potential of the Cu (i.e., the primarymaterial), namely, when the Cu is nobler than the Ru, the pH of theslurry is adjusted such that the corrosion potential of the Ru is setwithin a passive state area or a stable area on a Pourbaix diagram ofcopper. As a result, even if the potential of the Cu is pulled towardsthe Ru side, the Cu does not get drawn inside the corrosion area and theCu is reliably polished within the passive state area or the stablearea. Accordingly, it is possible to prevent corrosion of the Cu.Namely, even if a plurality of types of polishing material are exposedon a surface to be polished, it is possible to ascertain thereactivities of the electrochemical characteristics in relation to eachindividual one of the materials to be polished. Accordingly, it ispossible to predict the occurrence of unanticipated faults in the CMP200 such as corrosion of the material to be polished, over-polishing,defect creation, and the like, before these faults actually occur, andthus perform highly accurate polishing. Moreover, it is possible toalways maintain optimum control of the composition of a slurry, andachieve a stabilization of the polishing process. Furthermore, it alsobecomes possible to choose an optimum slurry using these evaluations, sothat the development of an optimum process in an even shorter timebecomes possible.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as limited by theforegoing description and is only limited by the scope of the appendedclaims.

For example; in the present embodiment, a description is given of whencopper (Cu) is used as the primary material and ruthenium (Ru) is usedas the secondary material in a wire forming method using a Damasceneprocess, however, the present invention is not limited to thiscombination and a variety of combinations are possible.

Moreover, it is not necessary for the sample material to be a thin filmin the same way as the material to be polished, and provided that it isthe same material, it is also possible for a thick film to be formed onthe substrate surface.

1. A polishing method in which, at the same time as a slurry is beingsupplied to a surface of a polishing pad by a slurry supply apparatus, amaterial to be polished is polished by moving the polishing padrelatively to the material to be polished that is formed on a substratesurface while also bringing the polishing pad and the material to bepolished into mutual contact, comprising: measuring a polishingcharacteristics by measuring electrochemical characteristics of theslurry in relation to the material to be polished; and preparing theslurry based on the measured electrochemical characteristics, wherein,in the polishing characteristics measurement, a slurry is supplied fromthe slurry supply apparatus, and using a sample polishing pad that isformed from the same material as the polishing pad and a sample materialto be polished that is formed from the same material as the material tobe polished, the electrochemical characteristics are measured both whenthe sample material to be polished is being polished by the samplepolishing pad and when the sample material to be polished is not beingpolished by the sample polishing pad.
 2. The polishing method accordingto claim 1, wherein, in the polishing characteristics measurement, theelectrochemical characteristics are measured using a plurality of thesample materials to be polished that correspond to a plurality of thesample materials to be polished that are formed on the substratesurface.
 3. The polishing method according to claim 2, wherein, in thepolishing characteristics measurement, the corrosion potentials of eachof the plurality of sample materials to be polished are measured, andwhen the corrosion potential of a primary material is measured in thepolishing characteristics measurement as being lower than the corrosionpotential of a secondary material from among the respective samplematerials to be polished, the composition of the slurry is prepared inthe preparation such that the corrosion potential of the secondarymaterial is set within a passive state area or a stable area of aPourbaix diagram of the primary material.
 4. The polishing methodaccording to claim 1, wherein, in the preparation, the pH of the slurryis adjusted.
 5. A polishing apparatus that is provided with a polishingpad, and a slurry supply apparatus that supplies slurry onto thepolishing pad, in which, at the same time as the slurry is beingsupplied by the slurry supply apparatus, a material to be polished ispolished by moving the polishing pad relatively to the material to bepolished that is formed on a substrate surface while also bringing thepolishing pad and the material to be polished into mutual contact,wherein there are provided a polishing characteristics measurementsection that measures electrochemical characteristics of the slurry inrelation to the material to be polished, and a preparation section thatprepares the slurry based on the measured electrochemicalcharacteristics, and wherein a slurry is supplied from the slurry supplyapparatus, and a sample material to be polished that is formed from thesame material as the material to be polished and a sample polishing padthat is formed from the same material as the polishing pad are held inthe polishing characteristics measurement section, and the polishingcharacteristics measurement section measures the electrochemicalcharacteristics both when the sample material to be polished is beingpolished by the sample polishing pad and when the sample material to bepolished is not being polished by the sample polishing pad.
 6. Thepolishing apparatus according to claim 5, wherein a plurality of thesample materials to be polished that correspond to a plurality of thesample materials to be polished that are formed on the substrate surfaceare held in the polishing characteristics measurement section.
 7. Thepolishing method according to claim 2, wherein, in the preparation, thepH of the slurry is adjusted.
 8. The polishing method according to claim3, wherein, in the preparation, the pH of the slurry is adjusted.